Oeatoeies



Oct. 8, 1929.

J. J. GILBERT TREATING LOADED SUBMARINE CABLES Filed Sept. l0, 1927 mjah! Patented Get. 8, 1929 tUNITED STATES PATENTv OFFICE JOHN J'. GILBERT, OF DOUGLASTON, NEVI YORK, ASSGNOR TO BELL TELEPHONE LAB- ORATORIES, INCORPORATED', OF NEYV YORK, N. Y., .A CORPORATION OF NEVI YORK TREAIING LOADED SUBMARNE CABLES Application filed September 10, 1&2?.

The present invention relates to means for improving the electrical properties of loaded submarine signaling conductors.

rlfhe continuously loaded conductor used in submarine signaling cables consists of a central copper Wire surrounded by tape or Wire of magnetic material forming a thin layer, through which runs a helical air-gap. OW- ing to the presence of this air-gap the magnetic flux due to current in the central conductor may be resolved into two components, parallel and perpendicular, respectively, to the air-gap. The inductance of the conductor is determined under ordinary conditions largely by the value of the first of these components. A magnetic field of any lind or value impressed on the loading material gives rise to a flux which, in general, may also be resolved into components parallel and perpendicular to the air-gap. A given magnetic material responds in various degrees to a given magnetic field, depending upon the history of the material or upon the presence of other fields. It is possible, therefore, to affect the inductance of a loaded submarine cable by means of a magnetic field superimposed upon the loading material.

Another peculiarity of continuously loaded submarine cables becomes manifest in their operation. lt has been found that when continuously loaded cables are operated duplex, a lack of symmetry exists between the imbalances resulting from positive and negative closures of the key. This lack of symmetry is chiefly due to the dissimilitude and unequal variations of the loading material characteristics of the cable with respect to those of the artificial line, as Well as to the effect of the earths magnetic field upon the loading material of the cable.

A characteristic of loaded conductors of importance in submarine signaling is the increase of inductance and effective resistance with signaling current. Due to this phenomenon there are tivo undesirable effects present in loaded signaling cables. First, modulation occurs between parts of the same Vsignal or between tWodifferent superposed signals, resulting in distortion of the signals. Second, the effective resistance 1n the portion Serial No. 216,841.

of the cable adjacent to the transmitting terminal is so large, that the attenuation constant may be greatly increased above its value corresponding to small currents, and consequently the efficiency of transmission of the cable is decreased.

In applicants co-pending application, Serial No. 696,981, filed March 5, 1924, there is described a method of reducing the attenuation and distortion in a loaded signaling conductor by means of loading the cable more heavily in the central portions and more lightly at or near the terminals. In other Words, in accordance With that method the inductance of the cable is increased in the center portions and progressively reduced toward the end portions of the cable.

It has been proposed to subject loaded submarine cables during or after their manufacture to the demagnetizine action of alternating currents for the purpose of rendering the properties of these cables more uniform. See, for example British Patents 224,827 and 235,510. However, the objects of the present invention are not attained by deinagnetizing a cable by means of an alternating current alone. One reason, for example, Why this is the case is that any gain in inductance secured is likely to be neutralized by the subsequent handling of the cable.

Among the objects of this invention are to reduce the effective resistance and to increase the ratio of effective inductance to effective resistance of a loaded submarine cable; to reduce the variation of inductance with magnetizing current or magnetizing force; to reduce the distortion of signal Waves; to facilitate duplex balancing; and to render the properties of a loaded cable conductor more uniform.

Means and methods are provided for carrying` the above objects into effect during or after the laying of the Whole, or a portion, of a loaded submarine cable.

These and other objects and advantages, which Will be set forth hereinafter, are attained, in one aspect of the invention, by subjecting the loading material of the cable to the simultaneous influence of a properly selected unidirectional magnetic field, and a lUO superposed alternating held, the alternating iield being gradually diminished from a value sutticient to in'luence the loading material to Zero.

The distinctive features o't the present invention are set forth with particularity in the appended claims. Several examples of methods ot and means tor carrying the invention into effect Will noiv be explained in detail, in the following description, with rei:- erence to the accompanying drawings, in Which:-

Fig. l is an enlarged developed vieiv of the loading tape of a continuously loaded submarine siffnaling cable on a short length ot conductor Fig. 2 is a graph or the comparative results ot inductance measurements or' a continuously loaded conductor When subjected to Zero and considerable extraneous superposed yrial magnetic fields, respectively,

Fig. 3 depicts the comparative results ot measurements ot' the inductance and the resistance of treated and untreated continuously loaded submarine sample conductors at Various values of measuring current; and

Figs. l and 5 illustrate various modes of applying the present invention to loaded submarine signaling cables.

lt has been observed that the etlective in ductance of a loaded submarine cable conductor as a Whole, or of individual portions thereo', is knot invariable with current or applied magnetizing forces, but in fact, tends to vary as the applied magnetizing torce varies. The desirability of making the inductance more uniform in consecutive portions et trie cable and ot reducing the variation of inductance With magnetizing torce underlies the present invention. The invention is based in part upon the observation that treatment of a loaded submarine cable conductor by applying a unidirectional magnetizing torce of appropriate value to the loading material, and superimposing upon this an alternating inagnetizing torce, which alternating magnetizing torce is gradually reduced to Zero, tends to reduce the variation ot inductance With magnetizing force. An additional result ot the same treatment is that the ratio ol: inductance to resistance is increased.

Suitable methods ot applying superimposed unidirectional and alternating magnetizing forces are described hereinafter. rthese methods vary with respect to Whether the cable is long or short, laid or not yet laid, and other circumstances. There is some evin dence thatmagnetic materials may have man;x netic properties ditlering in one direction through their mass, and in another, and that these properties may vary in accordance with the previous history of thematerial. lV hen a signaling current is sent through a loaded conductor having loading material Wrapped helically thereabout, the permeability or the material in a direction following the helix is that which is important in establishing the properties of the conductor.

Any elongated conductor, unless it be placed perpendicular to the earths field, will have a component of the earths liel d eiective in a longitudinal direction. ln some cases, especially With high permeability materials, this component must be taken into account applying a unidirectional magnetizing torce to a conductor. A direct current lloiving through the conductor may set up a magnetization ellective to aid or oppose the magnetism due to the earths ield. For this and other reasons, it seems desirable to analyze `the relation oit the ma 'netic oliect in loading "3 material due to a current flowing therethrough, with respect to the magnetic effect the y due to'etrnal fields such as the earths field. ils `Jrcliminary mattei', thereiore, this relation will noiv be discussed.

For convenience the turns ot the helically applied loading strip may be considered as parallel strips. See Fig. l. The magnetizing :torce l-l due to a current l in the conductor is equal to OAI T Where l is the diameter of the central conductor. rllhe magnetizing torce H can be resolved into tivo components H1=H cos a H2=H sin a, parallel andperpendicular, respectively, to the edge of the tape. The ettective permeability in these two directions being a, and au, respectively, the resulting flux densities are B12/M71 and The effective permeability in the direction parallel to the tape ,al is the actual perme ability ,a ot the loading material, Whereas the eilective permeability perpendicular to the tape is given by the expression (wtMS) 7 (to being the Width of the loading tape) and is usually not greater than 0.1 a.

From Fig. l it can be seen that when a magnetizing torce 7L parallel to the axis ot the conductor (due, for example, to a lield in Which the conductor lies) is impressed upon the loading material, its eliiect can be determined by resolving it into a component parallel to the direction of the tape 71,1: 7L sin a, and a component perpendicular to the tape 712: 71. cos a.

lf ll and it are impressed simultaneously Cel the magnetizing torce along the tape will be H cos a-i sin a,

and the inagnetizing force perpendicular to the tape Will be H cos Orl-IZ sin a.

The variations of inductaiice and of elfective resistance due to electric and magnetic losses in the loading material are principally determined by the time rate of variation oi' the flux which results from the component oit magnetizing torce parallel to the direction oi the tape. Assuming that H represents the tield due to the signaling current, then since the flux density in the direction of the tape is equal to ,al (H cos @.-L sin a),

it is evident that even though the superposed magnetiziiig torce 7L is constant with respect to time, it Will influence the flux density, and consequently the inductance and resistance of the conductor, because oit the fact that the values of a, and of its time rate of variation depend upon the total magnetizing `torce.

From the above formulae We may draiv the conclusion that the resultant component ott magnetizing force in the direction of the loading tape oi' a signaling conductor may be varied by means ot a current in the conductor. Let us assume, for example, that it is desired to neutralize a magnetizing force in the direction of the loading tape, due to the presence ot a component ofthe earths field parallel to the conductor and of magnitude 7L. This can be accomplished in accordance With the present invention by means of a direct current in the conductor having a magnetizing torce of such value that H cos a-i sin 0F10,

Hgh tan U..

The direct current thus required for this neutralisation can easily be derived from the relation 0.4] H- d (l) It has to be borne in mind, however, that the application of the current must take place in the proper direction with respect to the direction of the earths field, so as to oppose it, or to reiniorce it, as the case may be.

Fig. 2 represents the dependence of the inductance of a loaded signaling conductor upon the magnitude oi' the extraneous superp-osed magnetic field. A current of constant frequency and of amplitude gradually diminishing to zero (the initial amplitude being about 0.5 amperes) Was sent through the conductor. For the purposes ot explanation, this treatment ot the conductor shall herein be referred to as stabilization. Curve A of Fig. 2 repreents the inductance measurements made after the magnetic material had been stabilized in the presence of a superposed unidirectional magnetic lield oit zero intensity, no further stabilization occurring during the course of these measurements. Curve B, on the other hand, represents the inductance measurements during which the superposed unidirectional magnetic lield Was l'irst set at a given value, the conductor being then stabilized in this ield andthe inductance measured. As it will be seen from the curves, the inductance of the conductor is increased by the mere presence oit tne supeiposed field, Whereas the inductance is decreased by stabilization of the magnetic material in the superposed field.

llig. 3 shows the results of nieasi-irements of the inductance and the resistance increment (diilerence between the ell'eetive and direct turrent resistances) et a loaded conductor at various values ot the measuring current.

A copper' conductor ot 2l feet (6&0 centimeters) length and .13 inches centimeters) diameter, loaded with .0088 inch X .053 iiicli (.223 min. X 1.6 nim. permalloy tape iras first subiected to direct current iields otll=0 gauss and l-l :1.3 gauss. Simultaneously an alternating current of c. p. s. Was superposed and the alternating current Was reduced to 0 trom values ranging between 0.5 ampere to 0.1 ampere. After this treatment the incruetance and resistance et the sample Were determined at various values of a measuring current of c. n. s. The graphical illustration ot the results oi" these tests clearly sets forth the advantages to be gained by employing a superposed field of a certain intensity for the pui'- pose of diminishing the variation of resistance and inductance in loaded submarine cables. Curves D and E, respectively, represent the results of measurements at various currentvalues of the inductance and resistance of the conductor stabilized in a direct current lield of .3 gauss. Curves C and F, respectively, show the results et inductance and resistance measurements or" the saine conductor when stabilized in Zero field. Summarizing the results of these tests and considering first curves C and D, the percentage increase in the case ot the tests represented by curve D is about halt the percentage increase represented by curve C, in going trom 0 current to maximum current. is to the resistance increase of curves E and l?, the resistance represented by curve F is increased eleven times, Whereas the resistance has been increased only live times in case of curve E. Although the results shown by these curves Were obtained for the special case of a magnetic field parallel to the airis of the conductor, they are of more general application, since any uniform magnetic field intersecting the conductor from any direction can be resolved, at every point in the loading material, into three components having directions parallel and perpendicular to the axis and tangential to the surface ot the conductor, respectively. Considering` each of these components in successive short lengths contained in a complet convolution oi loadingtape, it is seen that the component parallel to the axis is 'the only one that does not suier frequent change of magnitude and direction due to magnetic noles set up the loading material. lt will be appreciated, therefore, that the results shown in tne curves represent the effec produced by any ordinary field, the axial component of which has the values indicates..

lt has been shown that the inductance and the rate oit variation oic inductance With current can be controlled by stabilizing the conductor in tne presence of a superposed magnetic iield of suitable value. For any given cable the most desirable set oi values of these Wo characteristics depends upon the conditions under which the cable is to be operated. Since, in general, there Will be a component ot the earths field in the direction of the cable conductor, it Will be necessary, in order to obtain the desired unidirectional field in the loading material, to superpose on the component ot the earths field in the direction of the tape another field by means of a steady current in the conductor.

rlhe present invention may be applied to cables already laid, as Well as to cables being,- laid. ln its application to cables already laid We may distinguish its employment in connection with short and long cables.

ln the case of signaling cables having lengths not greater than a few hundred miles, the superposed current may be maintained during operation oi" the cable by means of a direct current source placed at one or both terminals. Such sources might be in series with transmitting` and/ or receiving apparatus connected to the cable, but miht he placed in series With large choke coils placed in shunt to transmitting' and/or receiving apparatus.

in the case et longer cabina auch as -sed in submarine tclegraphy, ior e. the superposed current voltage rit-fl, of itself or combined with the nal-Linn, that .the potenane. the ground Would i daino/e the bec cable insulath i. be suddenly impressed at one .i ci the cal-ale. The transient current near the ends ot the cable due to i surges applied to one or both of the terminals may be considerably larger than the steady direct current due to the saine value o applied potenti Fig. 5 illust-rates one possible arrangement tor practicing the inven` tion in such a case. The cablD i0 is connected over key il and tuned ci cuit l2 to the ground. ln shunt to this circuit is provided another circuit including,` key 18, a battery lli and a resistance l5. ln order to treat cable 10, key ll is closed first, then key 13 is closed. litter an instant oi time key il is opened. 'l-he closing` oit key'll impresses a direct current surge en the cable, and also sets up a damped oscil1 tion in the tuner. circuit which causes a damped alternae'ig current te liew into the cable. rEhe opening" oit key ll, as soon as the alternat' l 'lhis operation may be re` peated at suitable iiitervals, in order to keep the terminal sc tions, or the whole cable, in the desired conrnrion.

@ne modo o" practicing` the present invention during" the laying operation et the sub' l 1 p .1' A Y l murine calore will ou' be dl ibcd.

h ig fr, a section oi' ca l may represent the c is common i cables in sections o1" about si() miles and n to splice these sect *.vethe during` lthe process ot laying, i tien an) ronini calde seeton l. Assume, for in.4

lroin source 3. A or example, an cri current or the general order oi 'om .l to amperes and (30 cycles may be employed. l-Lowcver, a dillerent currL r Y I t intensity may 3e used it neces.` rion being that the leading mat -alilc has to be led. A i. i current in any mricular easily derived from the rela adjusts..

re. ll the :1lternating` current held may be gradually diminished and red uc-ed to zero. rihe cable section which has een thus treated may tiren be disconnected and spliced to anotheii sectifiin, ir any. The following section or sections are then treated in a sin'iilar manner, except ihn! the alterr `ting;` current intensity nir-.y bsso chosen as to taper its upon su l prent cable caole sections. 'lhe rieure, lill() miles or length, is nier-ely rgir-en because this is a coinmonly used length or cable made be'lore snlicinfr, and it is obvious that sections olf lenig; h

differing 'from this rieure may be treated.

is also evident that in using different values of direct current, the degree to which the in'- ductance is reduced, may be changed at different points of the cable, in order to .eradually reduce the inductance of the cable to- Wart the terminal section, thus tapered efiiect. Furthermore, the treatment, if any, of the subsequent cable sections may differ in this from the treatment f the first or central sections that alternating current of higher freque y, for example 120 cycles, may be employed. lly sochoosing the alternating current as to attenuate its intensity toward the cable end iarthest removed 'from the point of applicaion, the efilect of its use upon the first section or sections may be made small or negligible.

Furthermore, since for Well known reasons variations of inductance with current near the ends of a. long tahie are much more iinportant than in the middle portions, it may be sufficient in practice to treat one or tivo terminal sections only. Since cables may be laitA from both ends and joined in any intermediate point, treatment of the first one or more end sections at each end Will be practicable.

Another method of obtaining a unidirectional magnetic field. of given value is to lay out the route of the cable so that the portion which it is desired to influence is inclined at a suitable angle to the earths magnetic field. If then the loading material is stabilized by means of a superposed alternating current which may be applied either during or aifter the laying operation. the cable will be brought into the desired electric condition. The stabilizing treatment may be repeated at suit-` able intervals, if necessary.

It is known that certain diiiiculties in accurate balancing of loaded submarine cables are due to variations of: inductance with current. This is especially true of such variations in the head end of the cable. To the extent that. the present invention enables the variation of inductance With current to be reduced, the particular difficulties due to this cause are remedied by corresponding reduction in magnitude of the unbalance effects. In U. S. Patent #1,607,473, November 16, 1926, to J. WV. Milnor, there is described a system for electrically balancing long loaded submarine cables for duplex signaling. In accordance With the Apresent invention the treatments herein described may be applied to artificial lines such as that described in Patent 1,607,473, as Well as to any other line containing inductance coils, with an effect analogous to that accomplished in the loaded signaling lines themselves.

The novel features believed to be inherent in the invention are defined in the appended claims.

Vvhat is claimed is:

1. The method of modifying the inductance, and/or reducing the variation of inductance With current, and/ or increasing the inductance-resistance ratio of all, or one, or more parts of' a loaded submarine cable system, which consists in subjecting the completed cable or part, or parts, to the simultaneous influence of a natural or rtificially produced uni-directional field and a superposed alternating field, the alternating field being gradually diminished from a value sufficient to stabilize the loading material of said cable to zero.

2. The method of improving the inductance-current and resistance-current` characteristics of a continuously loaded submarine signaling cable, Which consists in simultaneously applying to said cable a unidirectional magnetic field, and an alternating field of at least the approximate intensity required to stabilize the loading material of said cable, and gradually reducing said alternating held to zero.

3. The method of improving the transmission characteristics of submarine conductors continuously loaded With astrain sensitive magnetic material, Which comprises subjecting said cable to the simultaneous influence of alternating and uni-directional fields, said alternating field being progressively diminished from a large value to a relatively small value While the uni-directional field is maintained.

4. The method of treating a terminal portion of' a loaded signaling cable, Which consists in simultaneously applying to said ca ble uni-directional surges of current of large amplitude, and an alternating current, and gradually reducing the alternating current to Zero during each surge.

5. The method which comprises laying a portion of loaded submarine cable at such an angle with respect to the direction of the earths magnetic field, that the component of said magnetic field Which is eflective in said loading material produces a desired unidirectional magnetic field superposed upon said portion, and producing upon occasion an alternating current of considerable value in said portion, and reducing said current gradually to Zero.

6. The method of treating the magnetic naterial of the inductance element in a duplex submarine cable signaling system including a balancing network, which comprises impressing upon at least a portion of the magnetic material employed in the sysposed alternating and direct currents there on, to improve the electrical characteristics thereof.

8. A. method Which comprises treating a laid section of a long loaded submarine cable With superposed alternating and direct currents to improve the electrical characteristics thereof, and employing for such purpose alternating currents of such frequency as Will he attenuated to such an extent before reach` ing adjacent sections as to have relatively little effect thereon.

9. rlhe method of treating a continuously loaded signaling cable during the operation thereof which method comprises subjecting the loading material to the simultaneous influence of a unidirectional and an alternating magnetizinp1` field and gradually diminishing` the alternating ield to zero.

ln Witness whereof, I hereunto subscribe my naine this 8 day of September A. D., 1927.

JOHN J. GILBERT. 

